I started an airflow study in Robber Baron a year ago which has been continued by Evelynn in it and other area caves. We monitored CO2 at several minute sampling intervals over several days. CO2 levels varied widely from a little over 1000 ppm to over 12000 ppm. The changes in CO2 concentration closely followed changes in barometric pressure and large CO2 changes could occur in as little as an hour. Thus a single point measurement, like some of the other ones mentioned, may not tell you much in a cave with airflow.
Another interesting factor is that after a strong pressure rise, like after cold front arrives in the winter months, there is a lag, often of a few days, before the CO2 starts to rise again, even after the pressure has fallen some. This suggests there is a reservoir or source of CO2 at some point beyond the known cave that requires some extended period of outflow to draw it out after a large amount of outside air has been pulled in. In the summer, the CO2 response is faster since there is a small daily pressure cycle that does not draw in as much outside air. Overall then, the air seems "worse" in the summer since there are fewer large pressure increase event to push "good" outside air into the cave. In many high CO2 caves that I have been in around San Antonio there are few significant organics to decompose, so I don't think that is the source. I tend to go with Jerry's #2 or #3 hypothesis. Around San Antonio, I suspect the water in the aquifer dissolving carbonates may be the source of the outgassing and that caves with some connection to it are the ones with the periodically high CO2 - ie. as the cave blows out it pulls up CO2 from much deeper areas up to near the surface and then pushes it back down when it blow in. There are several groups currently doing research in this area and one problem is the hostile cave environment reeking havoc in instruments left in over the long term (condensation, corrosion, etc.) Joe ---- jerryat...@aol.com wrote: > > Elevated CO2 is a common occurrence in Texas caves with the highest levels > typically being found in caves developed in the Ellenburger or Austin > Chalk formations. Both of these formations have low permeabilities, and it is > > conjectured that this impedes the ability of CO2, once it accumulates, to > absorb back into the rock/water portion of the formation. That said, even > caves developed in formations with higher permeability and/or restricted air > flow may have elevated levels of CO2; usually not in amounts that cause > physical distress. > > As to the cause of high CO2 levels, there are several possibilities: > 1.) microbial decomposition of organic matter > 2.) excessive degassing of CO2 from formation water at the water/air > interface > 3.) degassing and/or breakdown of carbonates due to hypogene fluids moving > up from depth (these fluids may be related to hydrocarbons or igneous > activity) > 4.) Excessive human respiration in restricted passages > > > Bill Elliott and Butch Fralia conducted oxygen (O2) and carbon dioxide > (CO2) studies in several Texas caves and found that the amount O2 and CO2 in > the cave air usually added up to approximately 21% of the total composition > of the air no matter what the relative proportions of the two gases were. > Normal air contains 20.9% O2 and 0.04% CO2 by volume. In caves with bad > air, the CO2 typically displaces the O2 proportionately so that if CO2 > levels > approach 4%, then O2 levels are usually 17%. It should be noted that this > relationship does not always apply ! > > > To test for CO2, use the BIC lighter test that Butch Fralia published some > years ago: > "I've followed the air quality measurement comments of the last few Digests > with great interest. Over the last nine years I've participated in a > volunteer cave research project at a Texas State Park. Of the 150+ caves on > the > park, the majority have some level of measurable CO2 accumulation ranging > from detectable to deadly. Over the course of this project, the state has > furnished air quality instruments for our use. One is an electronic oxygen > meter and a Draeger device. Using these instruments, we've taken literally > thousands of air quality measurements. > "The Draeger instrument was by far the most reliable. The problem with the > Draeger is the high cost of the tubes, of which one is expended with each > measurement and not reusable. The Oxygen meter has a probe that must cleaned > often and replaced about every three months. I don't know if later model > instruments have this same problem. The oxygen meters are calibrated on the > surface at 21% oxygen. It's easily knocked out of calibration while moving > through tight passage areas. > "Unless a caver is involved in a research project such as the one on the > state park, the cheapest and most reliable air quality instrument available > is a BIC lighter. It can be obtained for about $0.97 at any convenience > store and easily replaced when damaged or depleted. It's within the > budgetary > range of anyone who can afford to go caving in the first place. This may > sound like a cop out to the folks who've offered all the fine advice on air > quality instruments but......read on gentle caver! > "When caving in the Arbuckle Mountains, the BIC was the air quality > instrument of choice though at the time, no one knew how reliable or accurate > it > was at the time. > "During the course of the state park project, we became curious at what > oxygen levels the lighter would start reacting. Using the instruments we set > up a number of controlled experiments and verified them with a number of > repetitions over several years with different brands. > "The lighter will start reacting at 19.5% oxygen. The flame changes color > and a small gap will begin to be noticeable between the flame and the jet. > At 18% oxygen, the flame will burn about 1 inch above the jet. At 17% > oxygen, the lighter goes out and can not be relit. As mentioned earlier, > these > measurements were very repeatable and could be verified by anyone with the > instruments to do so. > "In our tests, 99% of the time the oxygen was displaced by an equal amount > of CO2, such that 17% oxygen = 4% CO2. This was not always the case! In > two caves, the measurements were typically out of balance where the CO2 was > 2% higher than indicated by the oxygen level. This was repeated over years > of data! At the very least, when the lighter no longer burns, STOP! > "I should mention at this point that the physiological effects of bad air > result from the CO2 rather than oxygen deprivation! Most cavers, unless > they are asthmatic, can tolerate 17% [O2] without much difficulty; they will > breath heavier than normal for the amount of work being performed. At CO2 > levels > 2%, the caver should cave slowly! Especially when climbing! High > CO2 > will result in a much higher rate of breathing, the skin will be flushed > to pink, and you feel hotter than you'd expect in a 68 degree cave. > Hallucination, panic and even passing out are typical reactions, especially > when > the CO2 level is greater than 4%. Coming back to the surface, headaches and > even severe nausea may be experienced. This can be prevented by stopping in > an area that has between 18% to 19% oxygen for at least 15 minutes before > moving on to normal air. Those of us who smoke seem to be able to handle > higher levels of CO2 than non-smokers since we're used to poor air quality > anyway. > "If you can afford it and want to play, buy the Draeger for a reliable and > accurate instrument, otherwise 'Flick you BIC!' (Fralia)" > _http://thelances.org/hr3/badair.html_ > (http://thelances.org/hr3/badair.html) > Jerry. > > In a message dated 6/13/2010 10:46:32 P.M. Central Standard Time, > back2scool...@hotmail.com writes: > > Someone ought to post more on this subject because of the potential for > Hazardous levels of Carbon Dioxide in many areas of Texas. > We seem to have been blessed with a lot of karst (Ellenburger primarily) > prone to generating high levels of CO2 in the warmer months. I can tell you > that it can certainly present a life threatening scenario where vertical > caving is concerned. > I have been in very low air while crawling around and it can be very > disconcerting but one can generally evacuate to better air or be assisted. > On > rope in still air it can most certainly become life threatening very quickly > when rappelling into a pool of Carbon Dioxide. I became severely > disoriented and made an emergency egress after fast rappelling 75 feet into > a cave > in Cedar Park and hitting the bottom in what was probably life threatening > levels of CO2. Had I not made it out it would probably have been a body > recovery and could have involved more than one person if another caver had > descended to aid me not knowing the nature of the emergency. > You should be aware that CO2 is a common occurrence in many caves and if > you are on rope descend with caution should you notice bad air. It doesn’t > mean it will be life threatening but the change can occur very quickly and > one needs to be prepared, should the air suddenly become extremely bad, to > change over and get the hell out post haste. > I know decomposition of organic debris is the primary cause in most caves. > Not sure what research has been done on this phenomena or why it seems to > occur mainly in many Ellenberger caves. Want to say this is an oil > bearing rock and CO2 may be the result of microbial activity? Any comments > on > this from someone in the know. > Scott > > > --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com For additional commands, e-mail: texascavers-h...@texascavers.com
